Under Engineering

[Mace Canute]

As you all know, I have a Mahindra 7520 that was bought with ML275 FEL and BH. The backhoe sits mostly, but the tractor with filled AGs, equipped for loader work comes in at 12K# or more - depending on the counterweight. A good % of the 1300 tractor hrs has been heavy loader work. The loader has been awesome as a unit, but now its starting to break pins.
,,,The pins are made from Gr5 1-1/8" bolt blanks. - Plenty strong. Trouble is, it turned out in some cases that it was easiest to apply grease from the end of the pin. Pins for these positions are modified by drilling them down the center, then drilling a small hole in at the midpoint to intersect. A shallow groove is machined around it here to promote distributing the grease. This is where the pin fails. Its still plenty strong, but fatigues and cracks at the stress riser. The pins on the bucket carrier and the rams of the curl cyls are modified this way. These are the ones at most risk since the the forces are reversing causing flexing back and forth. -- Ive broken 3 of the six and have replaced them -and now the rest- with solid pins. ... Things bend when these pins fail. The alternate arrangement for greasing is worth it.

Anyone have any ideas how the pins in these areas could have been made to still feed grease from the end, but be more durable?
,,larry

Eliminate the groove.

 

[SPYDERLK]

Cheaper too. One less machine operation.
... Or, the groove could be cut with a rounded end tool to the same [shallow] depth, but turning out several times as wide and blending with the pin surface. The cross hole should also be shaped at its outer end. -- All would be an improvement.

 

[DuckSlayer1017]

As you all know, I have a Mahindra 7520 that was bought with ML275 FEL and BH. The backhoe sits mostly, but the tractor with filled AGs, equipped for loader work comes in at 12K# or more - depending on the counterweight. A good % of the 1300 tractor hrs has been heavy loader work. The loader has been awesome as a unit, but now its starting to break pins.
,,,The pins are made from Gr5 1-1/8" bolt blanks. - Plenty strong. Trouble is, it turned out in some cases that it was easiest to apply grease from the end of the pin. Pins for these positions are modified by drilling them down the center, then drilling a small hole in at the midpoint to intersect. A shallow groove is machined around it here to promote distributing the grease. This is where the pin fails. Its still plenty strong, but fatigues and cracks at the stress riser. The pins on the bucket carrier and the rams of the curl cyls are modified this way. These are the ones at most risk since the the forces are reversing causing flexing back and forth. -- Ive broken 3 of the six and have replaced them -and now the rest- with solid pins. ... Things bend when these pins fail. The alternate arrangement for greasing is worth it.

Anyone have any ideas how the pins in these areas could have been made to still feed grease from the end, but be more durable?
,,larry

All metal has a fatigue life and it looks like the life on your pins is somewhere around 1300 hrs. I wouldn't worry about finding a pin without the grease slots because they are there to help distribute grease. Just replace all the pins every 1000 hrs any you shouldn't have any more problems. Eliminating the grease passage on the pins could lead to excessive wear on the bushings in your loader that is not something you want to deal with.

 

[SPYDERLK]

All metal has a fatigue life and it looks like the life on your pins is somewhere around 1300 hrs. I wouldn't worry about finding a pin without the grease slots because they are there to help distribute grease. Just replace all the pins every 1000 hrs any you shouldn't have any more problems. Eliminating the grease passage on the pins could lead to excessive wear on the bushings in your loader that is not something you want to deal with.

The new solid pins are getting greased. I put a grease fitting in the collar/bushing thru which the pin passes.

 

[LD1]

stronger material?

 

[SPYDERLK]

stronger material?

Gotta alleviate that stress riser. I just took a closer look at a pin that isnt broken. The groove is narrow, but is done with a rounded tool so they did recognize the issue. The finish of the cut is rough tho. A smooth wide cut would be better as it would spread the flex over a wider area.
,,, If I thot I had to run the grease down the pin I would modify it differently - Mill a shallow flat about 1/2" long midway on the pin by side cutting with a 1/4" burr. Drill the pin down the center far enuf to go comfortably past the flat. Drill from the flat to intersect the center hole. Radius the hole entrance on the flat. ... About the best I can imagine.
,,,, Ill take the solid pin any day if theres any way to make it work.
larry

 

[LD1]

I gotta agree with others, use a solid pin and dont worry about the groove. The grease will get where it needs to be.

And typically, the grooving that I do see, is done with a rounded tool. I wasnt aware that yours were square (like a snapring groove). Thats not a good design.

Are there bushing by chance? or just "eye" on the end of the cylinder? Alot of times I see grooving on the ID of a bushing or bore as opposed to in the pin itself.

 

[SPYDERLK]

I gotta agree with others, use a solid pin and dont worry about the groove. The grease will get where it needs to be.

And typically, the grooving that I do see, is done with a rounded tool. I wasnt aware that yours were square (like a snapring groove). Thats not a good design.

Are there bushing by chance? or just "eye" on the end of the cylinder? Alot of times I see grooving on the ID of a bushing or bore as opposed to in the pin itself.

Guess you didnt see my previous post. The groove is rounded, but far from optimal because it is narrow and rough cut.

The eyes have no bushings. As they become a little bell mouthed with use the grooved pin cant take it because of the abrupt strength transition in its middle.

 

[jaotguy]

designed and built an extension digging tool for a local farmer ( and good friend) ... hooked onto his FEL bucket ...

spec'd out the strains and stresses .... built it 2x as strong as it should have been ... 2 days later it came back bent to the side .... doubled up the material and chalked it up to experience ... came back after 4 days , pins and bushings were wearing fast and elongating ... doubled up on those too... a week later I get a call, his FEL bucket is tearing off at the top where the hydraulics attach... welded them back and put in gussets to beef things up ( not part of the original tool for him ) ... drove by a couple of days later and figured out the problem....

the extension tool dug well (too well) , but he had trees in the way, he was using the "extension" to hook the trees up higher and was pulling and pushing them over...then pulling them out of the ground like a BH would ..... extreme side loading, and stresses way over the original design for just digging ... a case where a unit was pushed well beyond the original intent .

I agree with the "bean counter" problem ... many things are well designed, but would last a lot longer if they use heavier bearings or added extra material in key places ... factory costs of a couple of bucks per, but it adds up over thousands built , the investors/owners get the benefits instead.

may OLD over built tractors ( and attachments) are still running today (and being abused )... keep on ticking ...
a lot of the newer stuff dies a quick death when asked to do the same.

a lot has to do with "right sizing" and weight reduction ( for the shipping costs ) .... use the smallest and lightest materials to do the job, with no room for extra safety margin.